18 Bordeaux Mixture and Plants 



presence of copper in the cnticlc of grape leaves which had been treated 

 with various strengths of copper sulphate solution : no information is 

 however given as to the condition of the leaves as regards injury. Rumni 

 {Ber. Deut. Bot. Ges. xi, p. 79) and later Crandall {loc. cit.) found no 

 penetration of copper from copper sulphate solutions through the cuticle 

 of uninjured apple leaves. Pickering on the other hand (loc. cit. p. 113) 

 showed the presence of copper in the ash of " perfectly sound " apple 

 leaves treated with various copper solutions. 



During the present investigation damaged apple foliage which has 

 been sprayed and which shows any signs of scorching has always been 

 found to contain some copper. Repeatedly, such leaves have been 

 examined. The procedure adopted has been first to wash the sprayed 

 surface in dilute acid, great care being taken to wet every portion with 

 a brush, then to transfer the leaves to running water for half an hour 

 or longer, after which they are dried and ignited and the ash tested for 

 copper. In the case of scorched leaves, copper is invariably found to 

 be present in the ash. On the other hand, with really uninjured summer 

 apple foliage, copper has not been detected in the ash^. Probably the 

 presence or absence of slight injuries is sufficient to account for the 

 conflicting results of other workers. 



A comparison of the results of dipping healthy summer and autumn 

 apple foliage into 5 per cent. CuSOj is very striking. As has been men- 

 tioned, the summer leaves are little affected by this treatment ; the 

 autumn leaves, however, besides being severely scorched, absorb a good 

 deal of copper which is passed down into the stem, killing all the interior 

 cells for some distance below the portion actually immersed. 

 Crandall has recorded a similar translocation of copper through the 

 stem of apple trees into which solutions of copper sulphate had been 

 injected through wounds. Browning of the leaves was also observed. 



It would appear that there is no absorption of copper through the 

 normal cuticle of a healthy apple leaf. Autumnal changes, however, as 

 already shown, lead to a partial change in the nature of the leaf 

 surface, and there is a varying amount of action of Bordeaux mixture 

 resulting in injury and absorption of copper. 



Turning now to the behaviour of potato foliage towards Bordeaux 

 mixtures, we find rather a different state of affairs. The cuticle appears 

 to be distinctly more permeable than that of normal apple leaves. On 

 covering potato leaves either with the ordinary or the " no-excess-lime " 

 mixture there is certainly some absorption of co])])or, for it can readily 



* By the ferrocyanide tr.st. 



